reserve U for Universe;
reserve x for Element of U;
reserve U1,U2 for Universe;

theorem Th90:
  for C,D being strict Category st C ~= D holds CatToSet C ~= CatToSet D
  proof
    let C,D be strict Category;
    assume
A1: C ~= D;
    C = SetToCat CatToSet C & D = SetToCat CatToSet D by Th87;
    hence thesis by A1;
  end;
